CJEE

Chinese Journal of Electrical Engineering ›› 2021, Vol. 7 ›› Issue (4): 3-14.doi: 10.23919/CJEE.2021.000033

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Evaluation of High Step-up Power Conversion Systems for Large-capacity Photovoltaic Generation Integrated into Medium Voltage DC Grids*

Shilei Lu1, Kai Sun1,*, Haixu Shi1, Yunwei Li2, Guoen Cao3   

  1. 1. Department of Electrical Engineering, Tsinghua University, Beijing 100084, China;
    2. Department of Electrical and Computer Engineering, University of Alberta, Edmonton AB T6G2R3, Canada;
    3. Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2021-09-30 Revised:2021-11-05 Accepted:2021-11-21 Online:2021-12-25 Published:2022-01-07
  • Contact: *E-mail: sun-kai@mail.tsinghua.edu.cn
  • About author:Shilei Lu (S'18) received the B.E. degree in Electrical Engineering from Southwest Jiaotong University, Chengdu, China, in 2017. He is currently a Ph.D. candidate in Department of Electrical Engineering, Tsinghua University, Beijing, China. His research interests include high efficiency DC-DC converters, multi-level converters, photovoltaic generation and micro-grid applications.
    Kai Sun (M'12-SM'16) received the B.E., M.E., and Ph.D. degrees in Electrical Engineering from Tsinghua University, in 2000, 2002, and 2006, respectively. He joined the Faculty of Electrical Engineering, Tsinghua University, in 2006, where he is currently a Tenured Associate Professor (Research Professor). From Sep. 2009 to Aug. 2010, he was a Visiting Scholar at Department of Energy Technology, Aalborg University, Aalborg, Denmark. From Jan. to Aug. 2017, he was a Visiting Professor at Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Canada. His research interests include power electronics for renewable generation systems, microgrids, and energy internet, high performance converters for hybrid AC/DC microgrids, power quality and distributed power generation system. Dr. Sun serves as an Associate Editor for IEEE Transactions on Power Electronics, IEEE Journal of Emerging and Selected Topics in Power Electronics, and Journal of Power Electronics. Dr. Sun served as the TPC Vice Chair of IEEE ECCE 2017 and IEEE ECCE-Asia 2017, the Organization Committee Chair of IEEE eGrid 2019, and the Publicity Chair of IEEE ECCE 2020. He also served as the General Co-Chair of 2018 International Future Energy Challenge (IFEC 2018). Dr. Sun serves as PELS Asia Pacific Regional Vice Chair, PELS Beijing Chapter Chair and PELS Electronic Power Grid Systems Technical Committee (TC8) Secretary. He was a recipient of Delta Young Scholar Award in 2013, and Youth Award of China Power Supply Society (CPSS) in 2017, and IEEE Transactions on Power Electronics' Outstanding Reviewers Award in 2019. Dr. Sun is selected as IEEE PELS Distinguished Lecturer in 2021-2022.
    Haixu Shi (S'16) received his bachelor's degree in 2014 and his Ph.D. in 2020, both of Electrical Engineering from Tsinghua University, Beijing, China. His current research interests include modeling and control of DC-DC and AC-DC interlinking converters in microgrid applications. He is a reviewer of Journal of Power Electronics, and IEEE Transactions on Power Electronics.
    Yunwei Li (S'04-M'05-SM'11) received the B.Sc. in Engineering degree in Electrical Engineering from Tianjin University, Tianjin, China, in 2002, and the Ph.D. degree from Nanyang Technological University, Singapore, in 2006. In 2005, Dr. Li was a Visiting Scholar with Aalborg University, Denmark. From 2006 to 2007, he was a Postdoctoral Research Fellow at Ryerson University, Canada. In 2007, he also worked at Rockwell Automation Canada before he joined University of Alberta, Canada in the same year. Since then, Dr. Li has been with University of Alberta, where he is a Professor now. His research interests include distributed generation, microgrid, renewable energy, high power converters and electric motor drives.Dr. Li serves as Editor-in-Chief for IEEE Transactions on Power Electronics Letters. Prior to that, he was Associate Editor for IEEE Transactions on Power Electronics, IEEE Transactions on Industrial Electronics, IEEE Transactions on Smart Grid, and IEEE Journal of Emerging and Selected Topics in Power Electronics. Dr. Li received the Richard M. Bass Outstanding Young Power Electronics Engineer Award from IEEE Power Electronics Society in 2013 and the second prize paper award of IEEE Transactions on Power Electronics in 2014.
    Guoen Cao received the B.S degree in Electrical Engineering from Shandong University of Science and Technology, Qingdao, China, in 2009, the M.S. degree in Electrical Engineering from Beihang University, Beijing, China in 2012, and the Ph.D. degree in Electronics System Engineering from Hanyang University, Seoul, Korea in 2015. He is currently an Assistant Professor of Institute of Electrical Engineering, Chinese Academy of Sciences. His current research interests include resonant and soft switching power converter design, high efficiency power supplies in renewable energy applications, wide bandgap semiconductors and application, and electric vehicles.
  • Supported by:
    *National Natural Science Foundation of China (51811540405, 52007096) and National Key R&D Program of China (2016YFB0900205).

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Abstract: With the increase of dc based renewable energy generation and dc loads, the medium voltage dc (MVDC) distribution network is becoming a promising option for more efficient system integration. In particular, large-capacity photovoltaic (PV)-based power generation is growing rapidly, and a corresponding power conversion system is critical to integrate these large PV systems into MVDC power grid. Different from traditional ac grid-connected converters, the converter system for dc grid interfaced PV system requires large-capacity dc conversion over a wide range of ultra-high voltage step-up ratios. This is an important issue, yet received limited research so far. In this paper, a thorough study of dc-dc conversion system for a medium-voltage dc grid-connected PV system is conducted. The required structural features for such a conversion system are first discussed. Based on these features, the conversion system is classified into four categories by series-parallel connection scheme of power modules. Then two existing conversion system configurations as well as a proposed solution are compared in terms of input/output performance, conversion efficiency, modulation method, control complexity, power density, reliability, and hardware cost. In-depth analysis is carried out to select the most suitable conversion systems in various application scenarios.

Key words: Photovoltaic generation, dc-dc conversion, medium voltage dc grid, large-capacity, ultra-high voltage transfer ratio